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Materials Science in Additive Manufacturing Laser absorption and printability of 90W-Ni-Fe

A B C

Figure 6. GO-RT models displaying different powder morphologies: severely agglomeration (A), uniformly dispersion (B), and deformation (C).

A B The above shows that homogeneous nanoparticle-coated
90W-Ni-Fe powder with high sphericity has the best laser
absorption behavior. Agglomerated nanoparticles make
beams reflecting between nanoparticles and reduce the
stability of absorption, and deformed particles weaken the
multiple reflections and reduce the laser absorptivity and
penetration.
Figure 7. Calculated laser absorptivity of different models (A) and To verify the above simulation results, the laser
standard deviation of the absorptivity (B). absorptivity/reflection of nanoparticle-coated powders
with different morphologies were tested (Figure 9). Two
Moreover, the interaction and penetration of laser sets of nanoparticle-coated 90W-Ni-Fe powders with
beams also have an important influence on the quality of different morphologies were prepared at different milling
LPBF printing [13,22,25] . To further investigate the effect of speeds or ball-to-powder weight ratios. The energy in
powder morphologies on the laser absorption behavior of ball milling increased with the increase of ball-to-powder
LPBF, analysis surfaces were established in both horizontal weight ratio or milling speed as shown in equation VII .
[28]
and vertical directions (Figure 8A), which were used to As seen in Figure 9, the laser absorptivity of different
compare spot tracking results and irradiance distribution nanoparticle-coated 90W-Ni-Fe powders decreased with
of different powder bed models. The track spot diagram on the increase of milling energy. Moreover, it decreased
the upper surface and the irradiance in the depth direction significantly when the milling energy was too high
of the powder bed were shown in Figure 8B, and it can be (matrix particle deformed). The trend of experimental
seen that tracking spots appeared outside the laser spot results was consistent with simulation, indicating that
range due to the optical effect of external diffusion, which the homogeneous nanoparticle-coated powder with
promoted heat conduction and thermal radiation . high sphericity has sound laser absorption behavior with
[14]
When the nanoparticles were uniformly dispersed laser absorptivity of 93.51%. Similar to what has been
and the sphericality of matrix particles was good, the reported, the values of measured laser absorptivity have
irradiance in the depth direction was the highest and the a certain increment compared with simulation . This
[16]
laser interaction on the upper surface was the strongest. can be attributed to the balance between complexity and
However, when the nanoparticles were agglomerated or reality when constructing the model, the nanoparticles
the matrix particles were broken or deformed, the laser in the model are less than the actual, so the ratio of spot
penetration was lower, and the laser interaction on the size to the number of irradiated particles is increased,
surface of the powder bed was weaker. Moreover, the reducing the laser absorptivity [8,22] . At the same time, the
laser beam tracking spot was significantly reduced when actual W powder has a higher surface roughness than
agglomerated nanoparticles adhered to matrix particles, particles in the model, which also increases the measured
which can be regarded as a certain masking effect . laser absorptivity [8,14,16,22] . Although the calculated laser
[14]
When the nanoparticles were agglomerated, the laser absorptivity of models is lower, the models still reflect the
absorptivity of the powder bed was the highest, but most laser absorption behavior during LPBF. Moreover, these
of the energy acted on nanoparticles, which weakened models can visualize some phenomena which are often
the interaction between matrix particles and laser, challenging to observe in real-time in a mesoscopic view,
reducing the laser energy acting on matrix particles [25,26] . providing a relatively in-depth physical analysis of laser

Volume 1 Issue 2 (2022) 6 http://doi.org/10.18063/msam.v1i2.11